Abstract:
There has been an increase in research on the genus Ceratocystis, particularly in Africa, in the past ten years. This is due to the fact that these fungi represent economically important pathogens of agricultural and forestry crops, causing diseases of, for example, coffee, cacao, sweet potato, taro, oak and eucalypt trees globally. Despite this, little is known about the genus in Ghana. During studies of wood rot and other fungi in Ghana, the oak wilt pathogen, C. fagacearum, was reported from native Ghanaian trees. Previous to this report from Ghana, C. fagacearum was only known from oak trees and only from the United States of America, making this report from unrelated hosts in Ghana, highly significant. However, some doubt exists as to the accuracy of this identification since the fungus was identified based only on morphological observations. This study aims to try and confirm the occurrence of C. fagacearum in Ghana by identifying Ceratocystis isolates collected from the same hosts and from the same areas in the country, using modern molecular techniques. Chapter one deals with an overview of the genus Ceratocystis, with a particular focus on its taxonomy and identification of species in the genus. The ecology and importance of Ceratocystis spp. is covered, including its movement and dispersal. A particular focus is also placed on information regarding the species that are known to occur in Africa, since this forms an important component of any quarantine system. The importance of Ceratocystis species as quarantine pests is, therefore, also discussed. This chapter concludes with a discussion of the features that enable Ceratocystis species to be listed as pests of quarantine interest. Generally, the specific identity of a pathogen is a pre-requisite for proper classification and an understanding of its ecology and impact. Chapter two aims to identify isolates of Ceratocystis collected from logs of native trees in Ghana, using DNA sequence data and multiple-gene phylogenies. In using sequence data, three gene regions, the internal transcription spacer regions (ITS), including the 5.8S gene, the Beta-tubulin (BT) and transcription elongation factor-1α (TEF), are considered to compare isolates from Ghana with previously described Ceratocystis species to determine their identity. This work was done over a period of five months using a collection of isolates from Ghana. Since the project was designed as a mini-thesis and was based only on a pilot study in Ghana, more research is needed to clarify the morphology, ecology, distribution and impact of Ceratocystis spp. on both native and non-native plants in that country. This is especially important since vast quantities of native timber are exported to Europe and other regions, forming an important basis of the economy of Ghana. Copyright
